In addition to the air, water is another important vital factor for sustaining life. However, water purificatrion can be a difficult task to be solved, especially for mount-climbing activities or for surival in remote underdeveloped areas, and reponsively there are already a variety of water purifiers to be developed accordingly that can be used for purifying rain water or/and polluted river water. Nevertheless, most of those water purifiers can be adapted for purifying and desalinating seawater. Thus, it is still problematic to obtain sufficient fresh water for personnel engaging in maritime activities, especially in time of disasters at sea. Consequently, it is important and vital for people drifting at sea waiting for rescue to have an effective, electricity-free, ease-to-operate and simple-in-structure portable filtration unit with seawater desalination ability which is able to desalinating and purifying seawater into drinkable fresh water.